The presence of oxygen in packaging is often undesirable for various reasons. For example, products from the medical technology or food sectors in particular require the absence of oxygen for reasons of shelf life or production. Examples include artificial nutrition and the gamma sterilization of dialyzers. This absence of oxygen is usually achieved through the absorption of oxygen by iron or iron compounds. Usually, a sachet (bag) is filled with iron powder in which the oxygen has access to the iron powder (absorber) via a membrane. The binding process is mostly irreversible here, so that the bound oxygen is not released again. This allows to achieve the absence of oxygen/freedom from oxygen in a predefined volume.
It is difficult to identify an oxygen absorber that has already used up its capacity for various reasons, such as leaking transport packaging or too long storage outside a protective atmosphere during processing. A resulting presence of oxygen in a product package, for example, has a negative effect on the quality and/or shelf life of a product packaged therein.
In order to determine the absorption capacity/capacity/residual capacity of the oxygen absorber/absorber and thus for the quality assurance of the product, it is necessary to be provided with a suitable parameter which is clearly related to the absorption capacity of a sachet.
Each sachet contains a defined amount of the absorbent/absorber (iron), which can bind a corresponding amount of oxygen according to stoichiometric laws. The occurring reaction is exothermic. The additionally bound oxygen leads to a mass increase of the sachet. The parameter “temperature” cannot be used because the sachet cools down to the ambient temperature after the exothermic reaction with the oxygen and a history of the temperature is not recorded. On the one hand, the parameter “mass increase” is difficult to determine due to the small change in mass and, on the other hand, due to manufacturing tolerances, each individual sachet would have to be recorded and marked immediately after its production and its mass determined before use. An increase in mass could (however not clearly) be attributed to a reacted absorbent or the bound oxygen.